Performance Of EGSB In High Concentration Of Sulfate Antibiotic-containing Wastewater Treatment And Of Activated Carbon Enhancement Mechanism

Sulfonamide antibiotics have been widely detected in major water bodies of China,while antibiotics pharmaceutical wastewater is the main source of antibiotics into water environment.Therefore,efficient treatment of pharmaceutical wastewater is the key to minimize the risk of antibiotics in the environment.Currently,the challenge of biological treatment for pharmaceutical wastewater is that the toxic inhibition by high concentrations of organic matter,sulfate and antibiotics in wastewater that results in poor effectiveness.It has been shown that sulfate-reducing sludge has good tolerance to antibiotics and can remove sulfate from pharmaceutical wastewater stably and efficiently,however,the removal efficiency of organic matter remains to be further improved.Besides,carbon-based electron shuttles such as carbon materials have good bioaffinity and redox activity,which could alleviate the toxicity inhibition of anaerobic biological system by antibiotics and enhance the removal of refractory pollutants.By establishing a carbon-based electron shuttle-sulfate reducing coupling system,the removal of COD,sulfate and antibiotics in anaerobic reactors can be enhanced,and the discharge of antibiotics to the environment can be reduced.In this study,the typical sulfonamide drug sulfamethoxazole（SMX）was selected and expanded granular sludge bed（EGSB）was employed to treat synthetic pharmaceutical wastewater to investigate the removal efficiency of SMX and SMX transformation interface process by different sulfate loading EGSB（named EGSB-H,EGSB-L and EGSB-N,respectively）to reveal the mechanism of SMX transformation and removal under multi-media interface;by establishing activated carbon（AC）-anaerobic biological coupling system,synergistic and efficient removal of COD,sulfate and SMX was achieved;by exploring the abundance of key functional genes,antibiotic resistance genes（ARGs）and their relationship with functional microbial communities,the potential molecular biological mechanisms of antibiotic removal in anaerobic biological systems driven by AC were revealed.The main research contents and findings are as follows:（1）The effects of increasing COD and SO₄^2-concentration of influent on EGSB treatment performance and changing inoculated sludge concentration on domestication time were investigated.Research showed that EGSB achieved the highest COD and sulfate removal at influent COD=2000 mg/L and SO₄^2-=1000 mg/L.Increasing the inoculated sludge concentration from 19022 mg/L to 38044 mg/L could shorten the domestication time from 266 to 170 days.Desulfovibrio was the dominant sulfate-reducing bacteria（SRB）after domestication,accounting for more than 97%of the total SRB.（2）The effects of different influent COD/SO₄^2-ratios and starvation treatment on EGSB treatment performance were investigated.Research showed that elevating the COD/SO₄^2-ratio can facilitate the removal of sulfate by EGSB,while no sulfate loading EGSB（EGSB-N）has higher COD removal efficiency.After starvation treatment,the sulfate removal efficiency of high sulfate loading EGSB（EGSB-H）decreased significantly.（3）The effect of increasing the influent SMX concentration on EGSB treatment performance with different sulfate loads was investigated.Research showed that increasing influent SMX concentration could enhance sulfate removal of sulfate-reducing sludge.The SMX removal rate of all EGSBs was over 99%when the influent SMX concentration was 1 mg/L,while it was more efficient for EGSB-N with increasing influent SMX concentration;sulfite reductase and cytochrome P450enzymes were the key enzymes for SMX degradation in sulfate-reducing sludge;Desulfovibrio was enriched with elevated influent SMX concentration（≤10 mg/L）in sulfate-reducing sludge.Archaea were enriched with increasing influent SMX concentration in anaerobic system and Geobacteraceae,a DIET functional bacterium,was enriched at high influent SMX concentrations（≥15 mg/L）;ARGs residues and horizontal gene transfer risk were higher in sulfate-reduced system than in anaerobic system.Archaea were enriched with increasing influent SMX concentration in non-sulfate load sludge that did not contain sulfate,and DIET-functional bacteria Geobacteraceae were enriched at high influent SMX concentrations（≥15 mg/L）;ARGs abundance and horizontal gene transfer risk were higher in sulfate-reduced sludge than in non-sulfate load sludge.（4）The effect of AC addition on the treatment performances of EGSB with different sulfate loads was investigated.Research showed that after the addition of 10g/L of AC,the COD,sulfate and SMX removal efficiency of EGSB with low sulfate load（EGSB-L）increased from 44.06%,66.04%and 87.49%to 77.61%,94.12%and64.86%,respectively,while the COD and SMX removal efficiency of EGSB-N increased from 53.32%and 55.41%to 97.93%and 99.15%,respectively.After AC addition,Desulfovibrio and Geobacteraceae were enriched in sulfate-reduced sludge and non-sulfate load sludge,respectively;AC significantly reduced the abundance of multidrug ARGs,which might be due to the decrease of the abundance of Raoultella,a potential host of multidrug ARGs;Metagenomic analysis suggests that AC may partially substitute the role of IV type pili and cytochrome C for extracellular electron transfer;Metatranscriptomic analysis showed that the energy metabolism in non-sulfate load sludge was dominated by archaea,which was significantly different from that of the bacteria in sulfate-reducing sludge.